There have been facilities referred to as “data centers” in recent years, which manage a plurality of servers and storages, and provide connection lines to the Internet, and maintenance and operation services.
In a data center, a plurality of servers, storages and the like are installed in a plurality of racks. A Layer 2 (L2) switch, which is referred to as “top-of-rack switch,” is installed at an ingress on a communication line of each rack. Each top-of-rack switch is connected to each of the plurality of servers or the plurality of storages that are accommodated in the rack, via a downlink line. In contrast, each top-of switch is connected to a router connected to the Internet, via an uplink line.
A plurality of virtual machines (VMs) are deployed in one or more physical servers accommodated in the rack, and operating efficiency of the data center may be increased in proportion to operating rates of the physical servers or the VMs. Accordingly, the top-of-rack switch desirably has no free port.
A current mainstream A L2 switch, which is a current mainstream, for the data center includes 1-Gbps×44 to 48 ports on the downlink side, and 10-Gbps×4 ports on the uplink side. In other words, in the current state, if all the ports of the top-of-rack switch are caused to operate, an amount of traffic on the downlink side exceeds an amount of traffic on the uplink side, which does not provide non-blocking communication. In other words, a process for sending the whole traffic on the downlink side to the uplink side cannot be performed, which may result in a frame being discarded.    Patent document 1: Japanese Laid-open Patent Publication No. 2002-198994    Patent Literature 2: Japanese Laid-open Patent Publication No. 2005-517328
In order to solve the above problem, for example, it is conceivable to increase the number of ports on the uplink side. The increase in the number of ports, however, leads to an increase in cost of the L2 switch, and thus is not preferred.
The above problem is a problem that may occur not only in the L2 switch used as the above top-of-rack switch, but also in the case where the maximum amount of upstream traffic exceeds the maximum amount of downstream traffic in a relay apparatus. Moreover, regardless of a situation as above, application of a communication scheme with good data transmission efficiency is generally desired.